CVE-2026-46527: cpp-httplib Null Dereference

Description

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.44.0, When the server has called Server::set_trusted_proxies() with a non-empty trusted-proxy list, an attacker can send an HTTP request that includes an X-Forwarded-For header whose value parses to no valid IP segments. The code path then executes get_client_ip(), which calls front() on an empty std::vector—undefined behavior in C++. On typical implementations this manifests as abnormal process termination (denial of service). With Sanitizers enabled, you get an explicit runtime diagnostic. This vulnerability is fixed in 0.44.0.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0028

Probability of exploitation

0.20%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

Vendor	Product	Versions
yhirose	cpp-httplib	< 0.44.0

References

Advisories & Patches

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-hg3g-vrg8-578g https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-hg3g-vrg8-578g

Exploits

https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-hg3g-vrg8-578g https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-hg3g-vrg8-578g

Frequently Asked Questions

What is CVE-2026-46527? +

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.44.0, When the server has called Server::set_trusted_proxies() with a non-empty trusted-proxy list, an attacker can send an HTTP request that includes an X-Forwarded-For header whose value parses to no valid IP segments. The code path then executes get_client_ip(), which calls front() on an empty std::vector—undefined behavior in C++. On typical implementations this manifests as abnormal process termination (denial of service). With Sanitizers enabled, you get an explicit runtime diagnostic. This vulnerability is fixed in 0.44.0. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-46527? +

CVE-2026-46527 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0028, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-46527? +

CVE-2026-46527 affects products from yhirose, specifically: cpp-httplib. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-46527? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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